Year 11 - Science
Activity and half-life calculations
Nuclear physics
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This pupil-friendly study guide includes a unit summary, clear notes, common mistakes, and quick questions with answers.
Unit Summary
This unit covers atomic structure, isotopes, radioactive decay, and half-life. It explores alpha, beta, and gamma radiation, nuclear fission and fusion, and the uses of radiation in medicine, highlighting differences between contamination and irradiation.
Lesson Summary
You will learn to interpret radioactive half-life graphs and make calculations using values of half-life.
Key Notes
- The amount (or activity) of a radioactive isotope repeatedly falls by half in equal amounts of time.
- A radioactive half-life graph shows the amount (or activity) of a radioactive isotope plotted against time.
- In 2 half-lives the amount (or activity) of a radioactive isotope falls to ½ × ½ = ¼ as much.
- In 3 half-lives the amount (or activity) of a radioactive isotope falls to ½ × ½ × ½ = 1/8 as much, and so on.
- Radioactive isotopes with short half-lives decay quickly, emitting most radiation over a short period of time.
Vocabulary To Learn
- activity: the number of decays per second; it is measured in becquerels (Bq)
- radioactive isotopes: contain unstable nuclei that will decay over time and emit ionising radiation
- radioactive half-life: the time taken for the activity of a sample of a radioactive isotope to halve
Common Mistakes To Avoid
- It is impossible to predict outcomes for random events such as radioactive decay.
3 Quick Questions (With Answers)
1. Explain the scientific idea in this lesson using two key points.
The amount (or activity) of a radioactive isotope repeatedly falls by half in equal amounts of time. A radioactive half-life graph shows the amount (or activity) of a radioactive isotope plotted against time.
2. Define this scientific word and use it in context. 'activity'
the number of decays per second; it is measured in becquerels (Bq). Include the word in a full scientific explanation, not as a single label.
3. Correct this common scientific misunderstanding.
Mistake: It is impossible to predict outcomes for random events such as radioactive decay. Correction: Use analogies to show that random nuclear decay can lead to predictable outcomes, such as the randomness in the order popcorn kernels pop, but the predictability of how quickly all the popcorn takes to cook.
More Lessons In This Unit
- Activity and half-life calculations (including complex ones) Study Guide
- Evidence of atomic structure Study Guide
- Ionising radiation Study Guide
- Nuclear decay Study Guide
- Nuclear decay (including beta–plus) Study Guide
- Nuclear fission and fusion Study Guide
- Nuclear power Study Guide
- Nuclear power stations Study Guide
- Radioactive half-life Study Guide
- Unstable nuclei Study Guide
- Uses of radiation Study Guide
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